Control device for rolling mill

ABSTRACT

In a rolling mill so constructed that top and bottom work rolls are bucked up by upper middle and upper buck-up rolls, and bottom middle buck-up rolls, respectively, and the adjustment of movement of the middle rolls in the axial direction is combined with the adjustment of bending of the work rolls to effect shape control of a plate material as rolled; a control device comprising means for detecting the rolling load and the width of the plate material, means for determining the optimum roll bending force and the optimum roll movement in response to a signal from the means for detecting the rolling load and plate width, means for detecting an actual roll bending force and an actual roll displacement, means for comparing the optimum values with the actual values, and means for controlling the roll bending device and the roll movement device in response to a signal from the comparator means.

tlmted Mates Patent [191 [111 3,%2,345 Shida 51 Sept. 2, 1975 CONTROL DEVICE FOR ROLLING MILL [57] ABSTRACT Inventofl shigel'll Shida, Hitachi, Japan In a rolling mill so constructed that top and bottom [73] Assignee: Hitachi, Ltd, Japan work rolls are bucked up by upper middle and upper buck-up rolls, and bottom middle buck-up rolls, rel l Filed? y 5, 1973 spectively, and the adjustment of movement of the [21 APPL 376,454 middle rolls in the axial direction is combined with the adjustment of bending of the work rolls to effect shape control of a plate material as rolled; a control device Foreign Application Priority Data comprising means for detecting the rolling load and July 7, 1972 Japan 47-67494 the width, of the plate material, means for determining Jul 7, 1972 Japan 47-67501 the optimum roll bending force and the optimum roll movement in response to a signal from the means for [52] us. Cl. 72/8; 72/247; 72/21 detecting the rolling load and plate Width, means for [51] Int. Cl B2lb 37/00; B2lb 31/18 detecting an actual roll bending force and an actual [58] Field of Search 72/247, 242, 243, 8, 6, roll displacement, means for comparing the optimum 72/245 values with the actual values, and means for control ling the roll bending device and the roll movement de- [56] Referen e Cited vice in response to a signal from the comparator UNITED STATES PATENTS means- 2,776,586 l/1957 Sendzimir 72/242 3,076,360 2/1963 Sendzimir 72/242 Primary Examirzer-Milton S. Mehr Attorney, Agent, or Firm-Craig & Antonelli 7 Claims, 9 Drawing Figures ROLL MOVING DEVICE L ROLL MOVING PATENTEDSEP' 2 1 3, s02 345 sum 1 n5 7 FlG.l

FIG. 2

L0 L2 L4 P (ton) PATENTEU SE? 1 75 22:11] 3 HF z FIG...

OPERA- CQMPARA- TOR TIONAL DETECTOR CALCULATOR TOR- I I I PATENTEDSEP 2191s 3,902,345

SHEET U I]? 7 FIG. 5

SHAPE DETECTOR WIDE DETECTOR CALCULATOR ADDIER 20 F0 L OPERA- THONAL 2! 22 UNIT OPERA- TlON UNH' IALRO MOVING CONTROL [AL ROLL Movme CONTROL ADDER Lo PATENTED SEP 21975 ROLLING LOAD P (ton) am [IF I FIG.

I l l PAIEIIIEII @975 $902,345

sum 5 a; 7

FIG, 7

CALCULATOR REDUCTION MEANS OPERA TIONAL UNIT Ag MOVING DEVICE PATENTED 21975 3,. 902,345

sum 7 0F 7 L (mm) F E G. 9 5 AP A REDUCTION AD T F NAL K N UNIT CONTROL DEVICE FOR ROLLING MILL BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a control device for a rolling mill or more in particular to a shape control device and a gage control device suitable for use with the shape control device for a rolling mill so constructed that the shape of a material, as rolled, is controlled by the adjustment of the roll displacement in the axial direction in combination with the roll bending action.

2. Description of the Prior Art Nowadays, there is an increasing demand for higher accuracy of thickness of rolled products. In spite of the fact that the uniformity of thicknesses of a rolled product in the longitudinal direction has reached a considerably high degree due to the rapid development of an automatic gage control, effective means for controlling the uniformity of thicknesses of a rolled product in transverse direction has yet to be developed. Well known means for controlling the flatness of the material in the transverse direction is by utilization of the bending action of the work rolls in a four-high rolling mill. This means has so far been used effectively to some degree, but the fact that the work rolls are bucked up by a pair of buck-up rolls almost over the full length thereof imposes a limitation on the corrective ability by bending the working rolls. As a matter of fact, this lack of the corrective ability results in the unsatisfactory quality of the rolled products. A poor configuration of the products to some degree has been admitted as being inevitable or otherwise the work rolls have been replaced by new ones having roll surfaces formed in different crown each time the width of the plate material to be rolled changes. Any of the abovementioned measures has been accompanied by the disadvantages of poor quality of products or higher cost.

In view of this, the research group including the inventors have developed a rolling mill as disclosed in US. Pat. application Ser. No. 224,550 filed Feb. 8, 1972 such that the distribution of load applied to the work rolls is adjusted by moving the work rolls in axial direction in accordance with the width of the material, so that the disuniformity of the thickness of the material as rolled is eliminated for different widths of the material. This rolling mill, however, necessarily requires more control elements for correction of the shape of the material as rolled and higher skill for operation control, resulting in a greater burden on the oper ator. Further, the axial movement of the rolls causes the mill constant specific to the rolling mill to be changed, thus adversely affecting the control characteristics previously established for the automatic gage control.

SUMMARY OF THE INVENTION This invention is intended to obviate the above mentioned problems and an object thereof is to provide a control device for the rolling mill in which both the roll bending force and the roll axial movement are exactly controlled thereby to achieve automatic and accurate shape control of the rolled material.

Another object of the invention is to provide a control device for the rolling mill which exactly compensates for the changes in the mill constant caused by the axial roll movement thereby to accomplish accurate automatic gage control operation.

In order to achieve the above-mentioned objects, the control device for the rolling mill according to the present invention is characterized by the combined use of adjustment of axial roll movement and roll bending ac tion for shape control of the material, so that the optimum axial roll movement and optimum roll bending force are calculated upon detection of the rolling load and the width of the material, and a device for adjusting axial roll movement and a roll bending device are operated on the basis of the results of the calculation.

Another feature of the invention resides in the fact that there is additionally provided an automatic gage control device of the BISRA type in Whcih the relationship between the axial roll movement and mill constant is stored in advance, whereby the thickness of the material is controlled on the basis of a mill constant derived from an actual value of the axial roll movement.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagram showing the essential parts of an example of the rolling mill to which the present invention is applicable.

FIG. 2 is a graph showing the relationship between the axial movement of the middle rolls and the shape of the rolled material.

FIG. 3 is a diagram showing the relationship between the rolling load and optimum bending force.

FIG. 4 is a diagram showing essential parts of an embodiment of the invention as it is applied to the rolling mill illustrated in FIG. 1.

FIG. 5 is a diagram showing another embodiment of the invention.

FIG. 6 is a graph showing mill stiffness as related to the axial movement of the middle rolls.

FIG. 7 is a diagram showing essential parts of an example of the rolling mill to which only the automatic gage control is applied among the devices according to the invention.

FIG. 8 is a graph showing the relationship between the mill constant and the axial movement of the middle rolls.

FIG. 9 is a diagram showing the essential parts of an example of the rolling mill to which an automatic gage control different from that shown in FIG. 7 is applied.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, explanation will be made of an example of the rolling mill to which the present invention is applied, with reference to FIG. 2. This rolling mill is of such a type that the middle rolls 3, 3' each disposed between one of the work rolls 2, 2' and a corresponding one of the buck-up rolls 4, 4 are moved in the axial direction in accordance with the width of the plate material 1 by means of axial roll moving devices 6, The shape control of the material in rolling is effected by the adjustment of axial movement of the middle rolls in cooperation with the roll bending action of the work roll bending devices 5, 5' so that the work rolls may provide a smaller gap therebetween at the center portion than at both end portions. Thus the rolling mill according to the invention is characterized in that the distribution of rolling pressure imparted from the back up rolls to the work rolls is changed by axial movement of the middle rolls 3, 3 thereby to prevent the work rolls from being bent by the rolling pressure in a direction opposite to the direction of bending by the work roll bending dcvice. In the process, the freedom of the end portions of the work rolls-is increased roll to increase rol bending function by the roll bending device, which combines with the prevention of the opposite bending of the work rolls to achieve more efficient shape control. The arrangement of rolls is not limited to that shown in the drawing, but in another example the work rolls may be directly bucked up by the buck-up rolls, so that the shape of the material as rolled is controlled by a combination of the axial movementof the buck-up rolls and the work roll bending action. In still another example. the work rolls themselves may be moved in the axial direction to achieve the same effect.

The graph of FIG. 2 showing the relationship between the axial movement of the middle rolls and the shape of the material is based on the actual measurements in rolling under the conditions of the work rolls 110 mm in diameter, buck up rolls 200 mm in diameter, middle rolls l'mr'n in diameter, each 300 mm long, plate material 150 mm wide, rate of reduction of 7t and one ton of roll bending force. Symbol oz in the drawing shows the ratio of length L of the abutted orcontacted portions of the upper and lower middle rolls to width B ofthe plate material, while ,8: AI/AI where Al is the difference in elongation between the center and the ends of the material when a is 2 or length I is equal to the roll length, and A1 is the difference in elongation or reduction between the center and theends of the material when the middle rolls are displaced axially. The more B approximates zero, the better shape of the material is obtained. It will be apparent from FIG. 2 that the movement of the middle rolls in the axial direction very sensitively affects on the shape of the material and that the optimum value of the ratio ,8 is obtained when a 1V or thereabouts.

In other words, the shape of the material should best be controlled maintaining the relation Taking into consideration various conditions of rolling works, some correction AL may be required and then the equation (1) may be replaced by -L=B+AL...(2)

Thus it is possible to determine the axial roll movement on the basis of this equation.

The relationship between the rolling load P and optimum bending force F when L B is shown in FIG. 3. Assuming that the width B of the plate material is constant, the relationship between optimum roll bending force F and rolling load P approximates astraight line and is expressed as F=aP+h...

where u and b are functions of width B. From this equation, it will be noted that the optimum roll bending force depends upon rolling load P.

A control device according to an embodiment of the invention which operates on this principle as it is applied to the rolling mill of FIG. 1 is shown in FIG. 4. Plate width B and rollingload P are detected respectively by plate width detector means 7 and load detector means 8, and on the basis of the detected values B and P the optimum axial roll movementl. is calculated by a calculator or an operational unit 9, the output of which is applied to the comparator means 10. At the same time, the optimum roll bending force F is calculated and applied to the comparator means 11 in like manner. On the other hand, the actual axial roll movement L is calculated by an operational unit 13 on the basis of the measurements obtained by the axial movement detector means 12 and 12 and applied to the comparator 10, while the actual roll bending force F is detected by the roll bending force detector means 14 and applied to the comparator 11. The comparator 10 compares the input L with L and applies an output to the-axial roll movement control means 15, which uses the applied signal to actuate the axial roll moving devices 6, 6. The comparator ll compares the input F with F and applies its output signal to the roll bending force control means 16, which utilizes this applied signal to actuate the roll bending device 5.

Thus according to the embodiment under consideration, the roll bending force and axial roll movement are both exactly controlled whereby accurate shape control is performed, thereby greatly contributing to an improved efficiency of rolling operation and improved quality of rolled products.

Referring againto the preceding embodiment, rolling load P in equation (3) above is obtained from the well known equation below.

where K is a deformation resistance of material to be rolled, B the width of the material, 1 the length of a part of the material in contact with the rolls and Q a coefficient. Thus it will be seen that in the shape control of the material, the optimum axial roll movement L and optimum roll bending force F are determined by equations (2) and (3) above depending on the grade of steel making up the material, plate width, plate thickness, rate of reduction, tension and roll diameter.

The device according to the present invention may be modified as shown in FIG. 5. In the drawing, reference numeral 20 shows a calculator or operational unit which calculates the optimum axial roll movement L optimum roll bending force F and optimum plate shape 5,, on the basis of the grade of steel to be rolled, plate width, plate thickness, rate of reduction, tension applied to the steel plate and roll diameter and the like input data and applies them, together with plate width B to adders 21, 22, 23 and 24. The plate shape is represented by a valve B as abovementioned, or may be represented by a difference between the maximum thickness and the minimum one measured along a narrow portion of the rolled portion extending across its width or a ratio of those values. The optimum plate shape S is determined based on experimental data for such values. The adder 21 concerned with the roll bending force receives through a switch 27 optimum value F theactual roll bending force F from the roll bending force detector means 14 and an output AF as described hereinafter, from the operational unit 26 through a switch 27. The switch 27 is so operated that it opens in preset state and closes during a rolling oper ation. The adder 21 calculates and produces as an output the error signal E whichis This error signal is applied to the roll bending force control means 16 whereby it performs a control operation.

The operational unit 13 determines the actual axial roll movement L in response to an output signal from the axial movement detector means 12, 12' and applies a signal representing value L to the calculator 22. The calculator which is concerned with axial roll movement receives signals L and L and an output signal AL as described hereinafter, from the operational unit 28 through the switch 29. The switch is such that it opens in a preset state and closes during a rolling operation. The calculator 22 calculates and produces the error signal E below.

This error signal is applied to the axial roll movement control means 15 thereby to control the axial roll moving devices 6, 6'.

As the switches 27 and 29 are open prior to a rolling operation when the operators preset the roll bending force and axial roll movement, both AP and AL in equations (5) and (6) are zero, so that the control means 15 and 16 operate till the values F and L calculated by the calculator 20 coincide with values F and L respectively, and stop the operations when the coincidence is achieved.

During the rolling operation, both the switches 27 and 29 are closed, so that shape signal S produced from the shape detector means and width signal B produced from the plate width detector means 7 are applied to the adders 23 and 24 respectively. The adder 23 compares the signal S with signal S and applies an error signal AS to the operational unit 26. The operational unit 26 converts signal AS into a correction value AF or roll bending force and applies it to the calculator 21. The roll bending force F is corrected by AF according to equation (5). This means that the optimum roll bending force F calculated by using various parameters of rolling works as abovcmentioned is necessary to be replaced by a corrected value F AF due to various factors unforeseen. On the other hand, the calculator 24 compares signal B with signal 8,, and produces an error signal A8,, which is applied to the operational unit 28, whereupon the operational unit 28 converts signal AB into corrected value AL of axial roll movement and produces its output to be applied to the calculator 22. The axial roll movement L is corrected by AL in accordance with equation (6). In this connection, the component elements surrounded by a dashed line may be replaced by a single controlling calculator.

It will be understood from the above explanationlhat according to the present invention both the roll bending force and axial roll movement are capable of being preset simultaneously prior to the rolling operation, whereas they can be corrected during the rolling operation, thereby making possible accurate, automatic shape control by means of appropriate compensation of both the values.

where D is a roll gap index, 11 an intended thickness of the plate material delivered, W a relative value for mill spring, K a mill constant, and S an index equivalent to zero roll gap. Mill constant K is variable in a rolling mill according to the present invention which involves axial roll movement. Accordingly, in addition to rolling load P, mill constant K is required to be detected and substituted into equations (7) and (8) above thereby to control roll gap index D. According to the present invention. for the purpose of detecting the mill constant K, the axial roll movement L is made quantitatively related to mill constant K and thus the roll gap index D is controlled according to the axial roll movement L.

The relationship between rolling load and relative value of mill spring as the axial movement of the middle rolls is changed in the rolling mill of FIG. I is illustrated in FIG. 6. The shown graph involves axial roll movement L of 2000 mm for curve A, 1515 mm for curve B, 1020 mm for curve C and 500 mm for curve D in a rolling mill comprising work rolls 500 mm in diameter, buck up rolls 1500 mm in diameter, and midle rolls 650 mm in diameter, each 2000 mm long. As will be seen from FIG. 6, the axial movement of the middle rolls has a close relation to the relative value of mill spring, so that it is possible to determine the relative value of mill spring on the basis of such a relation measured actually, if the axial movement of the middle rolls is known in advance. Further, by substituting the relative value of the mill spring into equations (7) and (8), roll gap index D is determined.

An example of the application of the automatic gage control according to the invention to the rolling mill of FIG. 1 is shown in FIG. 7. In. this drawing, axial roll movement L is calculated by the operational unit 13 on the basis of measurements obtained from the axial movement detector means l2, l2, and the calculated results are applied to the calculator 40. The calculator 40, which stores a mill stiffness curve actually measured in advance about the rolling mill involved, calculates relative value W of mill spring corresponding to input L thereto, further calculates roll gap index D from input values W and P on the basis of equations (7) and (8), and then applies its output signal to the reduction means 41, whereupon the reduction means maintains a predetermined thickness of the plate material in response to input signal D.

Mill constant K included in equation (8) represents the gradient of the mill stiffness curve of FIG. 6 and when variations are taken in equations (7) and (8).

AD=AP/K....

From this equation, it can be said that if the thickness of the material is to be controlled successfully, the rolling load must be continuously detected and the roll gap index requires to be changed by AD on the basis of equation (9) when the rolling load varies by AP, An actual example of the relationship between axial roll movement L and mill constant K is shown in FIG. 8. As is apparent from the graph of FIG. 8, the mill constant K of equation (9) changes as a function of axial roll movement L.

The control device embodying the present invention which is applied to the rolling mill as shown in FIG. I on the basis of the above-mentioned relationship is illustrated in FIG. 9. In this drawing, it is seen that axial roll movement L is calculated by the operational unit 13 from the measurements obtained in the axial movement detector means 12, 12 and the output of the operational unit 13 is applied to the function generator means 50. The function generator means 50 applies mill constant K to the operational unit 51 on the actually measured relations between the axial roll movement L and mill constant K. On the other hand, rolling load P is continuously detected by the load detector means 8, so that variation AP is applied to the operational unit 51. The operational unit 51, calculating vari ation AD of the roll gap index from an input value K and AP on the basis of equation (9), applies its output to the reduction means 41. The reduction means 41 is actuated in response to input signal AD thereby to maintain a predetermined thickness of the plate material.

It will be understood from the above explanation that according to the present invention variations in mill constant in accordance with the axial roll movement are exactly detected. so that the setting and correction of the roll gap prior to and during the rolling operation is possible on one hand while both shape control and automatic gage control by axial roll movement are achieved at the same time on the other, thus greatly contributing to improved efficiency of the rolling operation and improved quality of rolled products.

I claim:

1. In a rolling mill wherein shape control of a plate material as rolled is effected by the use of a combination the adjustment of axial roll movement and roll bending action; the improved control device comprising means for detecting a rolling load and width of the plate material, means for calculating optimum axial roll movement and optimum roll bending force, an axial roll moving device and a roll bending device operated on the basis of an output from said calculating means.

2. A control device according to claim 1, comprising means for detecting the rolling load and the width of the plate material, means for determining optimum axial roll movement and optimum roll bending force in response to an input thereto from said detector means, means for detecting an actual axial roll movement and roll bending force, means for comparing the actual values means of axial roll movement and roll bending force with the optimum values of axial roll movement roll bending force and means for controlling an axial roll moving device and a roll bending device in response to the output signal from said comparator means.

3. In a rolling mill wherein shape control of a steel plate as rolled is effected by the use of a combination the adjustment of axial roll movement and roll bending action; the improved control device so constructed that the values of optimum axial roll movement, and optimum roll bending force and a value representing the optimum shape of the steel plate are determined on the basis of data including the grade of steel, standard width of the steel plate, thickness of the plate, rate of reduction, tension applied thereto and roll diameters, the width and a value representing the shape of the steel plate are detected, and the detected values are compared with said standard width and the value representing said optimum shape thereby to correct said optimum values of the axial roll movement and roll bending force.

4. A control device according to claim 3 comprising means for determining the values of the optimum axial roll movement, and optimum roll bending force and a value representing the optimum shape of the plate upon application thereto data required for shape control including the grade of steel, standard width of the plate material, thickness of the plate material, rate of reduction, tensile strength and roll diameters, said means producing said determined values and a signal representing the width of the plate material, means for controlling the axial roll moving device and the roll bending device in accordance with the optimum values of the axial roll movement and the roll bending force, means for detecting the width and a value representing the shape of the plate, means for comparing said detected values with the standard width and the value representing the optimum shape of the plate material and determining the correction values of axial roll movement and roll bending force and means for applying said correction values to means for controlling the axial roll moving device and the roll bending device.

5. In a rolling mill wherein shape control of a material as rolled is effected by the use of a combination the adjustment of axial roll movement and roll bending action; the improved control device so constructed that the mill stiffness characteristic varying with the roll movement in axial direction is memorized in advance, the axial roll movement is detected and converted into a corresponding mill stiffness characteristic in a rolling operation, and the roll gap is adjusted in accordance with the detected values of the mill stiffness and the rolling load.

6. A control device according to claim 5 comprising means for detecting the axial roll movement, means for comparing said detected value with the mill stiffness characteristic and converting said detected value into said mill stiffness characteristic, said mill stiffness characteristic being stored in said comparator means in advance, means for calculating a roll gap required for a material to be rolled into thickness in accordance with a rolling load separately detected, and means for reducing the rolls in response to a signal from said calculator.

7. A control device according to claim 5 comprising means for detecting an axial roll movement, function generator means for comparing said detected value with a mill constant and converting said detected value into said mill constant, said mill constant being memorized in said function generator means in advance, and means for calculating a roll gap variation required for maintaining a predetermined thickness of the plate material in accordance with the output from said function generator means and a rolling load separately detected, said calculating means applying its output to roll reducing means. 

1. In a rolling mill wherein shape control of a plate material as rolled is effected by the use of a combination the adjustment of axial roll movement and roll bending action; the improved control device comprising means for detecting a rolling load anD width of the plate material, means for calculating optimum axial roll movement and optimum roll bending force, an axial roll moving device and a roll bending device operated on the basis of an output from said calculating means.
 2. A control device according to claim 1, comprising means for detecting the rolling load and the width of the plate material, means for determining optimum axial roll movement and optimum roll bending force in response to an input thereto from said detector means, means for detecting an actual axial roll movement and roll bending force, means for comparing the actual values means of axial roll movement and roll bending force with the optimum values of axial roll movement roll bending force and means for controlling an axial roll moving device and a roll bending device in response to the output signal from said comparator means.
 3. In a rolling mill wherein shape control of a steel plate as rolled is effected by the use of a combination the adjustment of axial roll movement and roll bending action; the improved control device so constructed that the values of optimum axial roll movement, and optimum roll bending force and a value representing the optimum shape of the steel plate are determined on the basis of data including the grade of steel, standard width of the steel plate, thickness of the plate, rate of reduction, tension applied thereto and roll diameters, the width and a value representing the shape of the steel plate are detected, and the detected values are compared with said standard width and the value representing said optimum shape thereby to correct said optimum values of the axial roll movement and roll bending force.
 4. A control device according to claim 3 comprising means for determining the values of the optimum axial roll movement, and optimum roll bending force and a value representing the optimum shape of the plate upon application thereto data required for shape control including the grade of steel, standard width of the plate material, thickness of the plate material, rate of reduction, tensile strength and roll diameters, said means producing said determined values and a signal representing the width of the plate material, means for controlling the axial roll moving device and the roll bending device in accordance with the optimum values of the axial roll movement and the roll bending force, means for detecting the width and a value representing the shape of the plate, means for comparing said detected values with the standard width and the value representing the optimum shape of the plate material and determining the correction values of axial roll movement and roll bending force and means for applying said correction values to means for controlling the axial roll moving device and the roll bending device.
 5. In a rolling mill wherein shape control of a material as rolled is effected by the use of a combination the adjustment of axial roll movement and roll bending action; the improved control device so constructed that the mill stiffness characteristic varying with the roll movement in axial direction is memorized in advance, the axial roll movement is detected and converted into a corresponding mill stiffness characteristic in a rolling operation, and the roll gap is adjusted in accordance with the detected values of the mill stiffness and the rolling load.
 6. A control device according to claim 5 comprising means for detecting the axial roll movement, means for comparing said detected value with the mill stiffness characteristic and converting said detected value into said mill stiffness characteristic, said mill stiffness characteristic being stored in said comparator means in advance, means for calculating a roll gap required for a material to be rolled into thickness in accordance with a rolling load separately detected, and means for reducing the rolls in response to a signal from said calculator.
 7. A control device according to claim 5 comprising means for detecting an axial roll movement, function genErator means for comparing said detected value with a mill constant and converting said detected value into said mill constant, said mill constant being memorized in said function generator means in advance, and means for calculating a roll gap variation required for maintaining a predetermined thickness of the plate material in accordance with the output from said function generator means and a rolling load separately detected, said calculating means applying its output to roll reducing means. 